Alternating-current electromagnet.



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7 APPLICATION HLED DEC. M1915.

Patented Feb. 55,1918.

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DAVID C. LARSON, OF YONKERS, NEW YORK, ASSIGNOR TO OTIS ELEVATOR COMPANY,

OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ALTERNATING-CU'RRENT ELECTROMAGNET'.

Specification of Letters Patent.

Patented Feb. 5, 1918.

Application filed December 1, 1915. Serial No. 64,446.

7 To all whom it may concern:

Be it known that I, DAVID C. LensoN a. citizen of the United States. reslding 1n Yonkers, in the county of Westchester and ing of the secondary conductor, and in theconstruction and relative arrangement of the core and conductor.

An object of the invent1on is the prov1- sion of an alternating current electromagnet.

which is cheaply constructed and which will have great power with minimum current consumption.

Other objects of the invention will appear hereinafter, the novel combinations of elements being pointed out in the appended claims.

In the drawings, Figure 1 illustrates in front elevation an embodiment of my invention with brake apparatus; Fig. 2 is a side view of the same having one of the magnet cores removed; Fig.3 is a diagrammatic view of the magnet of Fig. 1; Figs. 4 to 14, inclusive, are diagrammatic views showingvarious. modifications of the invention; Fig. 15 illustrates a magnet with the usual arrangement of secondary winding or shading coil while Fig. 17 shows a similar magnet with the secondary winding arranged in accordance with my invention; Figs. 16 and 18 are vector' diagrams a P plied to the magnets of Figs. 15 and 1 respectively.

Like reference characters denote similar parts in all of the figures.

Referring more particularly to Figs. 1 and 2,1 show In invention applied to a magnet brake, suc :as is used connection with an elevator; the brake beigkg shown in released position with its magne energized.

The-brake comprises a brake pulley 1 and a pair of oppositely disposed brake shoes 2--2, which are carried by brake levers 3-3 pivoted at 44, to an A frame 5. A rod 6 passes freely through the lower ends of the levers 3-3, and carries a pair of compression springs 7'7, which bear against the ends of the brake levers and normally force the brake shoes into contact with the periphery of the pulley 1. The upper end of each brake lever 33 is connected by an adjustable link 8 to one of a pair of dashpot controlled arms 9, 9, pivoted at their upper ends to a stationary rod 23. To the lower end of each of the arms 9, 9, are bolted or otherwise suitably secured a series of laminae,-10, 10, which form the pole pieces or cores of an electromagnet. These pole pieces may be formed in many dilferent.

ways and, as here shown, they are similar to each other and resemble in plan view the letter E as indicated in Fig. 3. A magnet coil 11 which comprises the primary winding incloses the centerlimbs of each of the pole pieces 10, 10, and the spool containing this winding is suitably supported in fixed position. The outer limbs of each of the pole pieces are slotted at 17 to receive a conductor 12 comprising the secondary winding' which incloses a fractional part of the outer limbs of each of the pole pieces and also incloses the center limbs of the same.

In the particular. embodiment of the invention shown in Figs. 1 and 2, the conductor 12 comprises a rectangular strip of copper, brass or other suitable conducting material. One end of the strip conductor is secured to the metal frame of the magnet by the screws 13, while-the other end of the conductor is secured to the magnet frame by the screws 14. The intermediate portion of the conductor is'looped substantially one turn about a portion of the adjacent polar extremities of the outerlimbs of the pole pieces and the two loops 15 and 16 thus formed are wound in the same direction. The conductor also makes a half turn about the center limb of thepole pieces and, since the path of the current in the conductor is completed through the metal frame of the magnet, the conductor in effect makes a complete turn about the center limbs of the magnet and, as shown, this complete turn is wound in a direction opposite to that of the two loops inclosing the outer limbs of the magnet. While in this particular instance l have shown but a single turn about each of the adjacent polar extremities of the magnet, I contemplate using other than a single turn, depending largely upon the particular size and design of magnet and upon the use to which it may be put.

It will be observed that the conductor 12 is supported at either end so as to remain fixed in position, so that when the circuit to the magnet winding 11 is opened and the magnet cores become separated by] the pull of the brakesprings, the conductor 12 which forms .the secondary winding no longer embracesthe polar extremities of the magnet cores but remains unmoved within the air gap between the respective pole pieces. Upon energizing the primary winding, and before the pole pieces have moved to attracted position, the magnetic leakage is at amaximum and consequently the flux dens'ity in the secondary turns is at this time but a fraction of what it becomes after the cores'have come. into actual contact with the magnet is first closed.

each other. Hence it follows that the induced secondary current is relatively small upon first exciting the primary winding and so therefore the initial magnetizing currentsupplied from the mains will be very much less than it would be if substantially all of the primary flux were inclosed by the secondary winding such as one finds in the prevailing types of split phase magnets. This feature is 'of practical importance, in that it eflects a substantial saving of current, and-minimizes the usual disturbing effects on the main linewhen the circuit to Referring to Fig. 3, I show a variable resistanceelement 18 connected in the cir cuit. of the secondary conductor 12 by means of whichthe phase angle of the secondary current may be shifted and the flow of current controlled.

Fig. 4 discloses the same general form of magnet pole pieces as shown in Figs. 1

2 and 3, with a different arrangement the secondary winding. As here shown, the secondary-winding comprises two separate parts 12'and 12, each part consisting of a turn within the slot 17 which incloses a fractional part of the flux, and a turn about the magnet limb which incloses all of the flux passing in the limb. The resistances 18 and 18 may be included in the circuit of each of the separate parts of the secondary 12 and 12 if desired.

Figs. 5 and 6 are very similar to Figs. 3

and 4, respectively, the chief points of dif ference lying in the particular form of magnet cores used, and in the location'of the secondary windings. In these figures the magnet cores are made up of two unsym- .magnetic circuit induced by the primary winding is a single circuit as distinguished from the types of magnets shown in the preceding figures, in which the magnetic cir-, cuit induced by the primary winding is a divided or two part circuit.

Figs. 7 and 9 are similar to Figs. 4 and 6, respectively, as regards the arrangement of the primary and secondary windings. F1 s. 8 and 10 are very similar to Figs. 3 and 5, respectively, in that the secondary winding comprises two turns about a fractional'part of the main flux and also one turn about all of the main flux.

Figs. 11 and 12 represent an embodiment of the invention in connection with a well known type of solenoid magnet having a fixed core 19 and a movable core or plunger 20 which may be connected to give movement to any desired mechanism such as the pivoted-lever 21 adapted to ,move over a series of contacts 22. In Fig. 11, the secondary conductor 12 makes two complete turns about a fractional part of the polar extremity of the fixed core 19, and also one turn-about the entire polar extremity. In Fig. 12, the secondary conductor makes several turns inclosing a' fractional part of the flux in-the fixed core 19, and substantially one turn about each branch of the magnet frame which constitutes a double re- The improvements obtained by reason of my invention are best explained by means of vector diagrams applied to a split phase magnet havingthe usual shading coil and to a magnet embodying my invention. The

former is shown in Fig. 15; its secondary 12, which has one or more turns, is wound on a horn A formed by milling a slot in the right hand pole face. The primary coil 11 has only negligible resistance, so that the flux p which links with this coil may be considered as being constant under all con ditions. The flux (9 splitsinto a flux a, passing through A-and a flux o passing through the horn B, but the geometrical sum of q), and cp must always be equal to, o.

' and B but the flux q2 will be larger than the magnet frame and a The areas A and B will be assumed to be equal so that with open secondary e, and cp are equal ,to one half of q) and in phase therewith. The closed secondary, however,

the current flowing through the secondary will setup in A a magneto-motlve force opposed to the flux q, and actin as a screen toward the passage of lines 0 force through As a consequence, the flux q: will no longer be evenly divided over the areas A passing through B flux (p, passing through A. Moreover these fluxes will no longer be in phase with the flux qz. These phase displacements are however so small that for all intents and purposes they may be assumed as if they were each in phase with 9,, and as such in Fig. 16 OH will represent the phase qalinking Withthe primary coil 11, OB represents the flux o, and OA the flux c The flux p linking with the secondary, induces therein the electro-motive force e. represented by the vector OE, also linked with the secondary only is the leakage flux cp, represented by the vector OF, which causes in the secondary an electro-motive force of self-induction ED perpendicular to OF. When further OL is the vector of the secondary current. and OD represents the ohmic drop in the secondary, the triangle ODE expresses that the secondary induced electro-motive force OE is consumed by the electro-motive force of self-induction ED and the ohmic drop OD.

At instances at which the main flux q) is zero, rp, and. qa will also be zero, so that at such instances'the only flux which holds the armature sealed against the stationary part of the magnet is the secondary leakage flux 9 of which the instantaneous value will then be represented by OF, the projection of OF on the axis OY. In order to obtain there fore as large as possible a noiseless pull, we must evidently endeavor, for a given angle FgL, to make the flux q, as large as pos- S1 e.

Clearly nothing can begained by increasing the number of secondary turns, for, while the secondary induced electro-motive force will be proportional to the number of turns, the flux is inverted proportional thereto.

It will therefore be seen that for a given given primary excitation, the greatest possible noiseless pull is absolutely fixed. As is well. known this pull is comparatively small and when a large noiseless pull is desired unusually lar e and ex ensive magnet frames are require he principal object of my invention is greater noiseless pull been possible with a and a 'ven primar not only to obtain a than has heretofore given magnet frame excitation, but also to vary this pull at wi For this purpose I construct my secondary as, for example, in Fig. 17, having as in the previous example, one turn around the horn A, which is connected in series with another turn around the primary coil. Both turns are so connected that the electro-motive forces induced in them sum up.

Assuming the same primary excitation as with the ordinary split phase magnet of Fig. 15, OH (Fig. 18) will again be the veotor of the total flux linking with the primary coil which-splits into the flux OA :q) passing through A and the flux OB==qJ passing through B. As before the flux cp, linking with the secondary turn will induce therein the electro-motive force OE lagging 90 behind OH. The secondary turn around the primary coil links with the total flux OH and induces therein the electro-motive force OGr=E in phase with 6,. The total electro-motive force in the secondary is therefore si -FE, represented by the vector OK.' The fundamental difference with the usual arrangement of secondary is now evident. In that case the secondary leakage flux q), corresponded to the elcctro-motivc force Z, and one single secondary turn. In

the present case we have also one single turn which links with the leakage fluxqa but the electro-motive force will now be e f-E Other conditions being the same, the flux a, with my arrangement will be larger in the ratio and since the pulls are proportional to the square of the flux, the noiseless pull with my invention will be larger in the ratio ..+nE, T and the noiseless pull would have increased by the ratio (e.'+nE,

It will therefore be clear that with my invention obtain not only a larger noiseless usual form of magnet,

pull than is heretofore possible, but that by increasing -the number of secondary turns around the total primary flux I am in a position to adjust this pull to the requirements of the case.

I find that by reason of the-novel arran gement of the secondary conductor shown in the various figures, I am enabled to produce a magnet having a far greater economy and a much greater pull with a given exciting current, thanone arranged in any of the known ways. Furthermore, a magnet constructed according to my invention may be built at a fraction of the cost of the since the pull is so great and the phase splitting so perfect that the pole pieces do not have to be carefully fitted and hence a large amount of labor may be saved.

Without limiting myselfto the precise construction and arrangement of parts herein disclosed, what I claim is:

1. An alternating current electromagnet comprising a core, a primary winding, and a secondary conductor having a portion 1nclosing the total flux in said core and another portion inclosing a fractional portion only of the flux.

2. An alternating current electromagnet comprising a primary winding, and a secondary winding having a turn inclosing the main flux and another turn inclosing a portion only of said flux, said secondary turns being connected in series with each other.

3. An alternating current electromagnet of the type set forth comprising a core having a recess in its polar extremity, a primary coil, and a secondary winding having a turn, in said recess and another turn around the primary.

4:. An alternating current electromagnet of the type set forth comprising a magnet core having a recess in its polar extremity, a primary coil, and a secondary winding comprising a turn in said recess and a turn name to this specification 6. An alternating current electromagnet .of the type set forth comprising a magnet core having a recess in its polar extremity, a primary coil, and a secondary winding comprising .a turn in said recess and a turn around the primary, said turns being so connected that their induced electro-motive forces act cumulatively.

" 7. An alternating-current electromagnet comprising a primary winding, and a secondary winding having a turn inclosing the main flux and another turn inclosing a fractional part only of the main flux, said turns being connected in series with each other 'so thattheir induced electromotive forces sum up.

8. An alternating current electromagnet comprising'a primary winding, and a secondary or shading coil having series connectcd portions, one :of which incloses the total flux and another of which incloses a portion only of the total flux.

9. In an alternating current magnet, a secondary circuit, comprised of several turns adapted to inclose substantially the total primary flux in the core of the magnet and a single turn adapted to inclose substantially only a fractional portion of the flux;

In testimony whereof I have signed my in the presence of two subscribing witnesses.

DAVID C. LARSON.

Witnesses:

WALTER O. STRANG, JAMES G. Barnum. 

